Dolphins are highly intelligent mammals, with an amazing ability to learn to understand our language. But as we gain more insights into their behaviour, we're also coming to suspect that they might have their very own language — or at the very least a complex system for communicating with one another.

A big question facing marine biologists today is whether we'll ever be able to understand what they're actually saying. Thankfully, science could help us to construct a dolphin Rosetta Stone — but it won't be easy.

And like us, they have large brains and the capacity for higher-order thinking. They live in hierarchical arrangements, engage in fission-fusion social arrangements (which means dolphins come and go between pods as they please), cooperate, and exhibit unique personalities.

They can also pass the mirror test (an indication that they have a strong sense of self) and are able to respond to commands issued from a television monitor (surprisingly, not a lot of animals can do this — including some primates).

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And as highly social and engaged mammals, they may also have similar communicative needs. We certainly know that they have the capacity to understand language, but what we don't know is how much of their language is their own.

Clicks, burst-pulses, and whistles

Dolphins clearly have the means to communicate, and they do so with various sounds, including whistles, burst-pulses, and clicks. Just exactly what they're saying with all these noises, however, remains a mystery — but after years of study, marine biologists are starting to get a sense.

And scientists believe the clicks are used for echolocation. This allows dolphins to examine their environment through sound, listening to the echoes returning from objects being struck by the clicks. They may also be used for communication, and marine biologists are studying them to understand if this is the case.

Burst-pulse sounds may indicate a dolphin's emotional state, ranging from pleasure to anger — but we haven't studied these types of vocalizations very thoroughly, and we still have a lot to learn about them.

And as for the whistles, people are still debating whether, or how much, of whistle communication is intentional as opposed to unintentional (vocalizing stress, for example). But one thing is becoming increasingly clear: The whistles may actually be the names of dolphins.

Signature whistles

Or at the very least, whistles may a way for dolphins to identify themselves. One person who is seriously considering this possibility is Princeton's Tara Thean who has worked with the Sarasota Dolphin Research Program. Thean has spent time with bottlenose dolphins trying to get a better understanding of how they might be using their whistles to call out to each other and communicate.

Thean tells io9 that dolphins may be using their whistles as a means to identify one another. "They are basically stereotyped acoustic signals that identify the caller," she says. "Dolphins acquire these distinctive whistles as early as one year old." Exactly how these "signature whistles" emerge, however, remains a mystery.

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Even after meticulous listening for weeks on end, Thean noted that the identification whistles were never random and always consistent. In fact, she listened to identification whistles dating back several years and a number of them remained exactly the same as the ones still used today.

Thean is curious to know how the dolphins acquire their signature whistles, and who in the group is responsible for creating them. To this end, Thean hopes to study whether or not dolphins are modeling their whistles off those individuals that they associate with in the early part of their lives and what relationship those individuals have with the dolphins; it could be the mother, a sibling, or even someone not related — Thean wants to find out.

As for the reasons behind the signature whistles, one possibility is the need for "cohesion calls". Dolphins don't live in stable groups, instead mingling in and out of various pods. "The fluidity of these groups creates a bigger need for dolphins to call and identify each other," Thean says, "Otherwise they'd lose each other while they're moving in and out of these groups." Interestingly, dolphins may also be able to imitate the signature whistles of other dolphins, an indication that they're calling out to one another.

Clicking and hunting

Another good place to study dolphin communication is by observing their remarkably complex hunting practices.

Take spinner dolphins, for example, who work collectively to hunt lanternfish. Groups of about 20 dolphins have been observed approaching concentrations of prey and then pulling into a tight circular formation. At the same time they sequentially swim up and down vertically — doing a kind of "wave," akin to fans at a sporting event.

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The dolphins then continue to tighten the circle and form units of 10 pairs. The pairs at one o'clock and seven o'clock will move in, feed for 15 seconds, and retreat back to the circle. Then the pairs at two o'clock and eight o'clock do likewise. This goes on for about five minutes, during which time each dolphin gets two opportunities to feed. In the midst of all this is a cooperative group rise to the surface to breathe, all the while maintaining the circle. Each dolphin takes one breath, and the process starts again. The cooperation and synchronization is uncanny, as any deviation from the process would cause it to collapse.

According to marine biologist Kelly Benoit-Bird, communication has to be involved for this to work. Researchers have noticed that dolphins don't use their whistles during these feeding exercises, which are typically only used during non-foraging times and when they're resurfacing. Instead, the dolphins use their clicking sounds, with the highest click rates taking place just prior to foraging.

It's not immediately clear if these clicks are being used exclusively for echolocation, or for something else. Unlike whistles, which are omni-directional, clicks are highly directional like a laser. Benoit-Bird believes that clicks may be used as a strategy to communicate only within the group and not to other potential lanternfish predators. More work clearly needs to be done.

Do the math

Another possible way of cracking the dolphin language code is to use math. In a Wiredarticle from last year, Danielle Venton took a look at the work of Laurance Doyle, a member of the SETI institute. Now, while that might sound like a strange place to study dolphins, the basic idea is that if we can crack the dolphin code, we may very well be able to figure out what extraterrestrials might say to us someday as well.

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To do so, Doyle uses information theory, which is a branch of math that looks at the structure and relationships of information. By using information theory, for example, it's possible to separate binary code from random 0's and 1's. It's through this kind of analysis that researchers know that dolphin calves babble like human babies, but that adults emit actual information. Doyle's work indicates that there is indeed some linguistic substance to the sounds generated by dolphins, and that they follow basic rules of grammar and syntax.

The next step is somehow decipher this information into something we can understand. Given that we don't have a dolphin Rosetta Stone, this could be a monumental task.

Indeed, looking at the growing body of research, it's not immediately clear that we'll ever know all the complexities of dolphin language and communication. But what is clear is that the ongoing research is unveiling some remarkable insights into the sophistication of dolphin communication and behavior. It's fair to suggest that, even if we never crack the dolphin language code, we're getting some fascinating snapshots into cetacean life.